Update Sources/GRPCCore/Documentation.docc/Articles/Generating-stubs.md

Co-authored-by: George Barnett <[email protected]>

Author: rnro

Sources/GRPCCore/Documentation.docc/Articles/Generating-stubs.md

@@ -57,7 +57,7 @@ are included in the target's source directory and that you have defined at least
 
 ### Configuration
 
-You must provide a configuration file in the directory which encloses all .proto files (in the same directory or a parent). 
+You must provide a configuration file in the directory which encloses all `.proto` files (in the same directory or a parent). 
 Configuration files, written in JSON, tell the build plugin about the options used for protoc invocations. 
 You must name the file grpc-swift-proto-generator-config.json and structure it in the following format:
 ```json